"parking fine"

My wife was in for day surgery which went on longer than anticipated. She was told that she could go home at 6.45,l went and got my van from hampstead heath to get her.we were not free to go until 7.45.I received a fine of £100 although her blue badge was displayed. Due to the stress we have paid the fine . expensive visit for a sick person. Sort yourself out royal free. ps how can a camera spot a blue badge.